1. Tap "Go to MLB.TV" via the T-Mobile Tuesdays App
Note, you must click the provided link in the T-Mobile Tuesday App to activate the offer (a unique redemption code will allow you proceed w/ the registration or redemption of promo).

2. Log in or register at MLB.TV with your current T-Mobile Tuesdays Phone Number
Note, make sure the number you provide matches the phone number you registered to T-Mobile Tuesdays. If not, you won't be able to get your free MLB.TV Premium.

Additional details
MLB.TV Premium is MLB's streaming service to watch every out-of-market game for the 2017.
The free subscription to MLB.TV Premium expires on February 28, 2018.
Once you've registered, you can access MLB.TV Premium on any compatible connected device using your MLB.com account.